Internet Explorer 5.5

I upgraded my laptop from IE 5 to IE 5.5.
I use WIN NT 4.0 as my OS, and Lotus Notes Mail as my e mail software. On IE 5.5, I opened properties, and went to the Program tab to add my e mail Lotus Notes Mail, but in the e-mail drop down menu I only have Eudora Light, Internet Mail, and MS Outlook. How can I add Lotus Notes Mail into the program tab and make it my default e-mail software?